Electromagnets, particularly for electromagnetic regulators



April 12, 1960 A. STAM'BERG'ER 2,932,775 ELECTROMAGNETS, PARTICULARLY FOR-t ELECTROMAGNETIC REGULATORS Filed. Oct.

ELECTROMAGNETS, PARTICULARLY FOR ELECTROMAGNETIC REGULATORS Andrew Stamberger, Brockley, London, England, assignor Application October 22, 1956, Serial No. 617,558

' Claims priority, application Great Britain October 26, 1955 Claims. (Cl. 317-165) This invention concerns improvements relating to electromagnets, intended particularly for electromagnetic regulators but applicable also to switches, relays and the like. An object of the invention is to provide simple temperature-compensation for such electromagnets, especially compensation for the effect upon the action of an electromagnetic regulator of variation of temperature of its winding.

In accordance with the invention, temperature compensation is provided for by controlling the efiect of temperature variation upon an air gap or gaps between parts of the core or between the core and armature. Thus, in the case of an electromagnetic regulator having a U- shaped core between the ends of whose limbs an armature moves when attracted, provision may be made for the distance between the said limbs to be controlled so that, for example, the air gaps vary in such a manner as to compensate for the effect on the regulation of such temperature variation in the winding of the electromagnet.

An arrangement of this kind may, for some purposes, be effectively combined with the use in per se known manner of a bi-metal temperature-compensation device or of auxiliary temperature-compensation windings on the electromagnet.

One manner of carrying the invention into effect will now be more fully described by way of example and with reference to the accompanying drawing, in which:

Figure l is a somewhat diagrammatic end elevation illustrating the core and armature of an electromagnet, and

Figure 2 is an exploded perspective view of a temperature-compensation arrangement in accordance with the invention for such an electromagnet.

The electromagnet illustrated is that of an enclosed electromagnetic carbon-pile regulator which. may be generally of the construction described in United States Patent No. 2,828,395, dated March 25, 1958. The magnet core 1 is of a U-shape and the armature 2 (Figure l) is arranged, when attracted, to move bet-ween the ends 3 of the limbs of the U with air gaps 4 between the inner pole faces of the said limbs and the armature. For this purpose, as described in the said specification, the armature is carried upon a clapper structure 5 which is mounted to rock about an axis located at 6 and behind the electromagnet, as viewed in Figure 1. The core 1, which carries the magnet winding or windings 7, is of stripwound construction and is provided with corner pieces 3', substantially as described in British Patent No. 725,793. The magnet is supported from the fixed structure 8 (Figure 2) of the regulator by the clamping of the core limbs, by means of studs 9, between claw-like parts 10 of the said structure and a U-shaped or horseshoe-shaped clamping plate 11. The studs 9 pass freely through holes 12 in the plate 11 and engage in tapped holes 13 in the parts 10. Positive location for the core on the parts 10 or on the plate 11 is preferably provided so as to ensure that the core will follow expansion movement of the parts 10 and the plate 11. This may be effected by dowels. Alter- United States Patent 0 1 2,932,775 Patented Apr. 12, 1960 natively, the lower studs 9 may be a close fit in the holes 12 and in holes in lugs on the comer-pieces 3 and in the holes 13 in the parts 10.

The limbs of the core 1, which possess appreciable flexibility on account of the strip construction, are tied together by material having a low coefficient of thermal expansion. For this purpose, the two ends of the lower claw-parts 10 adjacent to the ends 3 of the core limbs are shown connected together by a tie rod 15 of material having a lower coefficient of expansion than that of the structure 8. The similarly located ends of the clamping plate 11 are shown bridged by a flat tie bar 16, although this is not essential. The material of the tie bar has a lower coefficient of expansion than that of the plate 11. For example, with the supporting structure 8 and plate 11 made of a light alloy, which has a coefficient of thermal expansion about twice that of the ferrous material of the armature, the tie 'rod 15 may be made of a, magnetic material such as an alloy consisting of 36% nickel and 64% iron and the tie bar 16 of a non-magnetic alloy, such as that known by the trademark K-Monel, having a coefficient similar to that of iron. Alternatively, the plate 11 and bar 16 may be made in one piece of, say, non-magnetic iron or light alloy.

If either the supporting structure 8 or the clamping plate 11 is made of material, for example of light alloy, with an appreciably higher coefficient of expansion than the armature 2, the distance between the limbs of the core 1 would, without the use of the tie means 15, 16, increase disproportionately with the expansion of the armature upon increase in temperature and the width of the air gaps 4 between the pole faces and the armature would increase substantially. With the said tie means, on the other hand, the said distance will increase less than the armature expands, so that the width of the air gaps 4 will decrease and less excitation will be required for the same magnet pull. By this means, an effect compensating for the increase of resistance of the winding 7 with increased temperature can be introduced.

As compared with compensation by bi-metal devices, the above-described arrangement has the advantage that the components assisting in the compensating effect have a higher thermal capacity than bi-metal strips. They are thus better matched with the winding in this respect. Also adjustment of the rate of the main control spring of the regulator will not affect the temperature compensation as much as is the case when bi-metal strips acting on the said spring are used.

Various modifications can be made in the tie means 15, 16: The tie bar 16 may be replaced by a tie rod fixed in lugs on the clamping plate 11 and spaced from the magnet core. This tie rod could then be made of a magnetic material such as the above-mentioned nickeliron alloy. The tie 15 between the claw parts 10 may be omitted and the clamping plate 11 relied upon to produce the required variation of the air gaps 4 upon temperature change. In this case, the limbs of the magnet core 1 should be positively located in relation to the said plate.

The variation in the air gaps 4 may be increased, if that is required, by fixing the tie 15 in the claw parts 10 at a greater distance from the core 1. Expansion of the body of the structure 8 carrying the said parts then tends to cause the distance between the core limbs to be reduced.

The variation in the width of the air gaps 4 will affect the torque rate of the magnet with the result that the accuracy of the regulation may be affected by temperature. If it is necessary to avoid this, an arrangement such as has been described above may be used in combination with a bi-metal compensation device provided between the armature and the main control spring, for example as described in the specification first referred to above. With 'such a combination," increase in temperature can be made to result, on the one hand, in reduction of the air-gaps 4 and increase in the magnet torque rate and, on the other hand, in decrease in the tension of the spring and reduction in the magnet torque ratewhen'the excitatio'nis reduced to restore torque balance. Botheifects will contribute to temperature compensation and, if they are appropriately proportioned, the magnet torque rate can be made to remain substantially constant I An arrangement such as has been described for controlling the air gaps of an electromagnet may alternatively be used to avoid the undersirable change of magnet torque rate which is obtained when a bimetal compensation device acting upon the control spring is used alone.

The birnetal device maybe of any nature, for example of simple construction or of a composite construction as described'in the specification first referred to above. It may be found necessary to obtain the required overall temperature-compensation effect by the use of adjustable stops giving the bimetal device a suitable temperaturedeflection characteristic.

It is also possible to use auxiliary temperature-compensation windings on the electromagnet in combination with the temperature-compensation means described above. I

p I claim: I

1. An electromagnet comprising a magnetic circuit which includes a flexible yoke of U-shape and an armature movable with air gaps between the limbs of the yoke, and means for obtaining temperature compensation by controlling the distance between the said limbs of the yoke comprising a member which connects the said limbs and which has a thermal expansion different from that of the said yoke.

A e ,n

I I2. An electromagnet as claimed in claim 1, and comprising a flexible yoke-supporting structure and a tie member which acts upon the said limbs of the yoke through parts of the said yoke-supporting structure.

3. An electromagnet as claimed in claim 1, and comprising a flexible yoke-supporting structure, a clamping plate of U -shape securing the said yoke to the said supporting structure and tie members which act upon the. said limbs of the yoke through parts ofthe said supporting structure and clamping plate.

4. An electromagnet as claimed in claim 3, wherein the said supporting structure is provided with claw-like yokesupporting parts and the U-shaped clamping plate with limb parts, the said yoke being secured between the said claw-like parts and thesaid limb parts, and the said tie members connect together the said parts of the supporting structure and clamping plate respectively.

5. An electromagnet comprising a magnetic yoke of U-shape, an armature movable between the limbs of the said yoke, a flexible supporting structure to parts of which the limbs of the yoke are connected and temperaturecompensation means comprising a connection between the said limbs having a thermal expansion different from that of the supporting structure. a

References Cited in the file of this patent UNITED STATES PATENTS i 1,425,858 Hunt Aug. 15, 1922 1,716,808 Wallace June 11, 1929 1,891,702 Allen Dec. 20, 1932 2,387,127 Dodd Oct. 16, 1945 2,458,957 Neild Jan. 11, 1949 Ertl May 28, 1957 

